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Jack Spine writes "Engineers at the National Museum of Computing at Bletchley Park have rebuilt the Tunny machine, a key device used in decoding German High Command messages during the Second World War. The Tunny machine took a team of three people three years to rebuild. At the end of the war, Tunny machines were broken up and the components recycled, while the original circuit diagrams were destroyed or hidden. The team had to piece together plans for the machine from odd pieces of circuit diagram that had been squirreled away by engineers, as well as from the recollections of some of the original builders."

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TFA is a little light on information on the "Tunny" code breaker (Tunny is the nickname for the German Lorenz cipher machine), so here's the link to the wikipedia for further reading:
http://en.wikipedia.org/wiki/Lorenz_cipher [wikipedia.org]

I do applaud the team who spent many countless hours rebuilding such a machine, but I'm really curious as to the reasoning behind such an effort.

This is kind of like walking into an automobile museum and finding a replica of a Ford Model T, built with modern blended steels. It just isn't quite the same.

Except now imagine there were no existing Model Ts to use as a reference, no diagrams, no instructions on how to contruct it, the original machinery used to make the model T is all gone, and all you had to go off of was what they described, including people's memory from 70 years ago.

The thing your forgetting is that we didn't want any of our temporary allies to advance their code breaking tech on our backs. Since we had advanced in our tech they were obsolete but still valuable to other nations they were destroyed because we had no use for them but other countries may have. Lots of military grade electronics are repurposed or destroyed today for the exact same reason.

If no hint was given that those cipher systems had been broken, it could be plausibly hoped that other nations would adopt similar systems after the surrender of Nazi Germany, considering them secure. Sure enough, the Soviet Union soon cobbled together a similar system, probably inspired by captured equipment. One can only imagine the frisson of glee that ran through the cryptanalysts when they discovered they could re-apply techniques and breaks they had already honed against the Germans.

Oddly enough, the American counterparts to Colossus were never destroyed. Instead these became prototypes of commercial computing equipment, built by the likes of IBM.

History is full of examples of technology, developed by the Allies (primarily the British) that was abandoned at home, but pursued by the USA for commercial gain. Radar and magnetrons, gas turbine engines, vacuum tube (as opposed to relay) logic, supersonic flight, to name a few. The Canadians development of a supersonic fighter/bomber industry was also stopped with the cancellation of the Arrow [wikipedia.org], possibly at the request of the USA military aircraft industry.

Apparently a number of German code systems kept on being used after WW2 (and by nations other than Germany). At least part of the Bletchley Park inventory ended up in GCHQ were the machines were used into the '70s.

It's even better than that: captured German Enigma machines were sold to newly independant former colonies, for their new governments use. Since nobody outside the highest circles knew Enigma had been broken, it seemed like a good deal.
That is why most of the code breaking equipment was destroyed or spirited away, and the code breaking secrets kept until recent years!

And the Soviet Union adopted a teleprinter encryption system loosely based on the Lorentz (Tunny) and Siemens Geheimschrieber. Needless to say, the Soviets wouldn’t have adopted that kind of technology if they had known it had already been broken during the war, and thus what was (presumably) a huge insight into the USSR’s secrets would have been lost.

Does anybody know if they've put together/published a detailed set of drawings for this machine? Given how much work it was to create it and how cool/historically significant it is, it would be nice if the hardcore nerds among us could order copies of the detailed technical information.

That's unfortunate. I've been a couple of times, and had a knowledgeable guide each time.In winter, they have a small staff on weekdays, so not everything is open and you may get a dull guide. Weekends are better. Or go during the summer.

The Bletchley Park guys figured out how the Lorenz machines worked by decoding messages by hand. They then built the Tunny machines to emulate a Lorenz machine. The actual codebreaking was mostly done by a Heath Robinson machine (or later, a Colossus), this yielded the correct wheel settings. These settings were then entered in the Tunny machines, and these could be used to decrypt the day's Lorenz traffic.

I was at Bletchley Park last year and saw the Tunny exhibit. Didn't realize that they were still worki